I’ve opened up the comments on this post to everyone — feel free to share your weirdest (or scariest!) dream at the bottom of the post.
What was the last dream you remember having? Was it a good dream, or was it a nightmare?
If you’re anything like me, this is a difficult question. The content of my dreams almost always escape me within a few minutes of waking. I have always been a bit jealous of people who have frequent, vivid dreams. It seems like that would be a magical way to spend most nights. Then again, maybe it wouldn’t be if it was a terrible nightmare and you didn’t have much control over what was happening.
There’s a great deal of variation in what we dream about, how vivid the dreams are, and how likely we are to remember our dreams. But, everyone dreams. It’s a universal aspect of human nature. But, what’s it for? Why did we start dreaming in the first place?
Dreaming presumably does have some sort of function or is at least a byproduct of something that does. It is unlikely that entirely random neuronal firing during sleep would result in coherent audiovisual experiences, no matter how bizarre they might be. Sure, the plots of most dreams look like they’ve been directed by David Lynch, but they do appear to be directed.
Even if the story and the characters are a bit bizarre, the events and characters in dreams are usually recognizable as things that exist or could exist in the world. The worlds of dreams might be weird, but they are complex and arise from complex neuronal processes. When complexity and the appearance of specific design exists in nature, it’s usually a good idea to consider why it’s there.
The Threat Simulation Theory of Dreaming
One of the more interesting evolutionary theories of dreaming comes from Finnish neuroscientist and philosopher Antti Revonsuo. His Threat Simulation Theory of dreaming posits that a key function of dreaming is to run simulations of threatening scenarios.
These simulations allow our brains to rehearse threat recognition and avoidance behaviors while we sleep, improving our implicit responses to real threats when we are awake. Sometimes the threat in dreams may be very literal, like a person chasing you through down an alley. Other times, the aggressor may be more metaphorical, such as a large monster chasing you through the woods. In both cases, each types of dream follows a typical threat-simulation script of being chased.
This isn’t to say that dreams only serve as threat simulators — that’s obviously not true. People have all sorts of dreams that have nothing to do with threats. Revonsuo’s argument is simply that the ability to dream came from the adaptive benefits that threat simulation would have. In other words, dreaming about threats would have provided the strategic advantage that is generally required for a feature to evolve. Once the ability to dream evolved, then dreams may take on all sorts of forms, assuming they still retain their ability to simulate threats.
The theory has racked up quite a bit of evidence in its favor. Although we may dream about many different topics, threats make frequent appearances in dreams. And a dream doesn’t have to be a terrifying nightmare to include a simulation of a potential threat. Aggression, failures, and accidents are all common features of dreams.
According to some studies, nearly 3 out of every 4 adult dreams include at least one threatening event. In most cases, the dreamer is the target of the threats. Dreams with high threat content, such as nightmares, are also more likely to be remembered after waking up. This might allow the threat-related scenarios to not only be implicitly rehearsed, but also consciously considered after waking up and shared with others.
A key prediction of the Threat Simulation Theory is that real threats should more strongly activate the threat management system, which would in turn lead to an increased prevalence of threats in dreams. The data seem to support this. For example, children who have experienced trauma are more than twice as likely to experience threats in their dreams. These dream threats are also more likely to include aggression and be a threat to their life. Increased daily stress, which might be associated with increased daily threat-perception, also predicts greater instances of nightmares. Relatedly, people who have greater vigilance toward threats (i.e., anxious people) report a higher frequency of threats in dreams.
There’s also some evidence for the threat simulation theory of dreaming from more traditional societies. Anthropologist Thomas Gregor collected information about nearly 400 dreams from the Mehinaku in central Brazil. The Mehinaku believe that the dreaming world is a real world filled with monsters, spirits, and the dreaming souls of other Mehinaku.
The Mehinaku place great importance on the predictive power of dreams, with dreams often being interpreted as predictors of injury, illness, and death. Because of this, it is a cultural practice of the Mehinaku to recount their dreams to friends and family each morning. Coincidentally, this makes them the perfect participants for a study on topics found in dreams.
One intriguing finding from Gregor’s study of the Mehinaku dreams was the frequency of aggressive dreams. The Mehinaku have far more frequent threatening and aggressive dreams than Americans do. Nearly 60% of Mehinaku dreams contain threatening features. In dreams involving aggression, the dreamer was typically the victim of aggression. The aggressors in the Mehinaku dreams are the same types of aggressors they would see in the waking world; they were typically men or animals such as jaguars, dogs, snakes, and venomous insects.
Some differences between men and women’s threatening dreams also emerged. While women report more fear and anxiety in response to dangerous animals such as jaguars and wild pigs, men report greater fear and anxiety in dreams about organisms such as venomous insects and snakes. Gregor take note of this difference and suggests that in their dreams, men and women each fear the kinds of animals they have little defense against in the waking world.
Mehinaku women do not carry weapons and are at greater danger if faced with a large animal such as a jaguar. This isn’t as big of an issue with Mehinaku men who do carry weapons and are better able to deal with large dangerous animals. However, strength and hunting ability offer little defense against the venomous insects and snakes that haunt the dreams of Mehinaku men.
Nearly 60% of Mehinaku dreams contain threatening features. In dreams involving aggression, the dreamer was typically the victim of aggression.
The threats that the Mehinaku faced in their dreams tended to be those that they were likely to encounter and less equipped to overcome. This is right in line with what Revonsuo argues is the function of dreaming: to simulate threats as a form of mental rehearsal. Evolutionarily recurrent threats, such as dangerous men, snakes, and large carnivores made frequent appearances in the Mehinaku dreams. But of course, the Mehinaku didn’t just dream about any large carnivores or snakes — they dreamt about those that were ecologically relevant to them.
It will be difficult to really prove why dreaming exists. We’ll probably never have the smoking gun. However, the audiovisual coherence of dreams suggests that their existence isn’t just random firing of neurons. They likely originated for a reason. Of the theories that I’ve seen on the origins of dreaming, the threat simulation theory of dreaming is one of the most interesting and convincing. Morbid curiosity, it seems, may have some of its roots in our dreams.
Just as playing with fear in our waking lives might help prepare us for danger, so too might playing with fear in our dreams.
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Cool read. These are mysteries about dreams I always wonder about. Also that chart was funny in a weird way.
The last nightmare I remember having, which I’ve had many times, is that I’m on a high surface, usually either a cliff or skyscraper, and I’m constantly about to slip off. So maybe that ties into the threat simulation theory.
Keep up the interesting work.